These experiments attempt to develop an explicit description of the major transformations applied to visual signals as they are transmitted through the early stages of the visual system. This will not only aid in integrating and systematizing our knowledge of light and dark adaptation processes, but also help place these adaptational transformations in a context where they can be related to other aspects of visual processing. The experiments attempt to separate out multiplicative and subtractive types of adaptational processes and locate them relative to major retinal non-linearities. We currently have little understanding of what mediates these processes, how they act together to determine sensitivity, and what their relative contributions are. The action of these processes is investigated during the transition to a steady state of adaptation following an increase or decrease of illumination. In this proposal attention is focused on a subtractive mechanism identified in previous experiments. Specific questions addressed are: 1. How rapidly does the subtractive process operate to restore sensitivity following an increase in illumination? 2. Is the subtractive process mediated by spatial or by temporal differentiation of the signal, or both? What is the time course of these two components? Is a receptoral as well as a post-receptoral non-linearity required to account for the results? 3. Does the temporal differentiation precede or follow the spatial differentiation? 4. How quickly do the laterally mediated subtractive signals decay? Does visual persistence slow down the restoration of the dark adapted state? Other experiments involve the role of spatially antagonistic mechanisms in color appearance rather than in sensitivity control. They measure the change in color appearance as the spatial frequency of a grating pattern is increased and ask whether the change in spatial configuration produces a change in the relative outputs of luminance and chromatic mechanisms.